As shown in FIG. 1, a conventional two-dimensional capacitive touchpad uses a plurality of capacitance sensors X1, X2 and X3 in X-direction and a plurality of capacitance sensors Y1, Y2 and Y3 in Y-direction for touch detection, of which each capacitance sensor is constructed from a trace, with the layout of diamond shape to maximize the per trace area for both X-direction and Y-direction. This capacitance sensor layout has the X-directional sensor pitch PX, the Y-directional sensor pitch PY, the maximum X-directional sensor gap MXgap and the maximum Y-directional sensor gap MYgap, as designated in FIG. 1, and the maximum sensor gaps MXgap and MYgap are equal to the sensor pitches PX and PY, respectively. The capacitive touchpad identifies a touch of a conducting object by detecting the capacitance changes on the capacitance sensors X1-X3 and Y1-Y3, and the magnitude of a capacitance change depends on the area of the object projected on the capacitance sensors. If the maximum sensor gap is large, the detectable object location resolution will be low due to nonlinear response of the object induced capacitance change on different traces, and thus the calculated location will be trapped to the nearest trace center, resulting in poor linearity. For example, as shown in FIG. 1, when an object is at the location 10, although it touches the X-directional traces X2 and X3 and the Y-directional traces Y1 and Y2 simultaneously, the areas where it touches the capacitance sensors X2 and Y2 are larger than that of the others X3 and Y1, so the capacitance changes on the capacitance sensors X2 and Y2 are more significant than that of the others X3 and Y1, and as a result the calculated location of the object will be closer to the coordinates (X2,Y2). When the object moves along X-direction from the location 10 to another 12, even though the real Y-directional location of the object does not change, the Y-directional capacitance changes will jump violently, causing the calculated Y coordinate varying significantly and thereby a larger nonlinear response existing. Thus, the capacitive touchpad will have a lower locating accuracy.
Therefore, it is desired a capacitance sensor layout scheme for linearity improvement.